Dynamical effect in measurement of the exchange-bias field: A consequence of the slow-relaxer mechanism

We report on the temperature dependence of ferromagnetic resonance (FMR) measurements on NiFe/FeMn bilayer. This includes investigations about the angular distribution of the resonance, H(R), and that of the linewidth, Delta H. By considering the domain-wall formation model, the exchange-bias field, H(EB,FMR), is derived from the FMR measurements. The disagreements observed at low temperature between these values and the ones obtained from superconducting quantum interference device measurements, H(EB,SQUID), are discussed. We demonstrate that the negative line shift and the maximum of the linewidth of the FMR line are both perfectly interpreted through the slow-relaxer mechanism. This enabled us to elucidate the intriguing question about the yielding to different values of the exchange-bias anisotropy by both techniques.